Thermodynamic properties of fluids

The aim of this article is to provide a basis for the thermodynamic properties of fluids and their practical applications. The first paragraph recalls the three principles of macroscopic thermodynamics, as well as the definitions of the fundamental quantities characterizing a single- or multi-constituent system.

But macroscopic thermodynamics is an empty framework for the study of matter. In particular, it says nothing about the equations of state of the system's constituents. That's why the following paragraph deals with these equations of state, for the perfect gas and for the real fluid. A microscopic model of the gaseous state is briefly introduced, to show that, within its range of validity, it can be used to evaluate many useful quantities, such as heat capacities.

This is followed by a discussion of fluid state changes, i.e. gas-liquid transformations for a pure body and for a multi-component system (ideal solution and real solution), with a presentation of diagrams that provide a convenient qualitative and quantitative description of these state changes.

Two particular multicomponent systems are the subject of special study, because of their practical importance: humid air and fumes.

Finally, indications are given of the data sources and methods for estimating the quantities involved in the many applications of the general considerations developed in this article.